This invention relates to fused glass structures, and more particularly, to a high strength glass structure which is partially perforate, and to a method of making the same.
The present invention will have many applications completely unrelated to those disclosed herein and should therefor not be limited thereto. However, the invention has been found to be especially useful in the manufacture of channel-type electron multipliers. For example, one such multiplier is disclosed in U.S. Pat. No. 3,449,582.
In the past it has been the practice to produce a channel-type electron multiplier of a glass wafer perhaps with a one inch diameter, a thickness small in comparison to its diameter, and holes extending through the wafer.
Unfortunately, the holes are etched in the wafer after its circumference is ground round. This leaves jagged edges where holes are etched that are intercepted by the circular edge. The sharp points around the etched edge cause arcing when the wafer is mounted in an image intensifier or other electron tube.
Prior art wafers have also been difficult to handle in tube fabrication because they have been extremely susceptible to damage due to the tenuous jagged edges thereof.
It is also an outstanding disadvantage of a prior art wafer that the small projections at the edge thereof can and do break off after an electron tube containing the wafer has been completely processed. Thus, the wafer often poisons an otherwise good tube. The poisoned tube is then a total loss.
Only after a substantial effort was made, was the present invention made. Efforts were made prior to this invention to surround the wafer with a glass ring having a thermal expansion coefficient about equal to that of the wafer glass. However, after etching, the fused wafer and ring must be fired in a hydrogen atmosphere. During this firing the wafer and the ring invariably separated even though the firing temperature never exceeded the annealing temperature of the wafer glass or the annealing temperature of the ring glass.